The present invention relates to a structure and method of forming a semiconductor assembly using adhesive materials to secure semiconductor dies to support elements without forming adhesive fillets.
In order to reduce the size of semiconductor devices numerous techniques have been developed to vertically stack one semiconductor die, hereinafter xe2x80x9cdiexe2x80x9d, on top of another die. FIG. 1 illustrates a conventional method of vertically stacking two die 20, 30 on a support structure 10, such as a printed circuit board (PCB) or other thin support structure, to form a conventional semiconductor assembly 100. The first die 20 is shown secured to a support structure 10 by an adhesive material 22a using techniques well known in the art. When the first die 20 is pressed against the support structure 10 the adhesive material 22a is partially forced outside the die""s 20 perimeter 29 and forms an adhesive fillet 24a. Likewise, when the second die 30 is secured against the first die 20 by an adhesive material 22b a second adhesive fillet 24b is also formed.
Both the first die 20 and second die 30 are shown wire bonded 40 to an electrical contact area 18 on the support structure 10. The first die 20 has an electrical contact area 28, such as a bonding pad, on its top surface 26. Because adhesive fillet 24b is formed when the second die 30 is secured to the first die 20, it limits the placement of the first die""s 20 electrical contact area 28. The distance B between the perimeter 39 of the second die 30 and a first die""s 20 electrical contact area 28 must be increased by distance A, the width of the adhesive fillet 24b, to provide sufficient operating space for the wire bonding equipment. Typical dimensions for distances B are about 428 microns or greater to allow for adhesive fillets 24b, which are conventionally about 228 microns in width or greater. Using current wire bonding equipment, distance B between electrical contact area 28 and the perimeter of the fillet 24b can be reduced to about 200 microns or less. In other words, adhesive fillet 24b requires about 228 microns or more of first die""s 20 top surface 26 on each side of the first die 20. If the adhesive fillet 24b were eliminated the space could be used either to increase the size of the second die 30 or to reduce the size of the first die 20.
An alternative method of stacking dies 20, 30 to a support structure 10 to form a semiconductor assembly involves using an adhesive film sized and aligned with the respective die 20, 30 perimeters. Since the adhesive film is cut or dimensioned with the second die""s perimeter 39, no adhesive fillet 24, as described above, is formed. However, adhesive films are expensive and are difficult to align with the dies 20, 30 and support structure 10. Accordingly, there is a need and desire for an easy, low-cost method of securing one or more semiconductor dies 20, 30 to various support structures 10 to form a semiconductor assembly 100 using adhesive materials 22 such that no adhesive fillets 24 are produced, for example, when a second die 30 is pressed and secured to a first semiconductor die 20 and when a first semiconductor die 20 is pressed and secured to a support structure 10.
The present invention provides a method to vertically stack at least one semiconductor die on top of another semiconductor die using an adhesive material without forming an adhesive fillet at the second die""s perimeter. An adhesive material is deposited over about 50% to about 90% of the top surface of the first semiconductor die, such that when the second die is secured against the adhesive material and first die no adhesive material extends past the perimeter of the second die. Because no adhesive fillet is formed, the distance between the electrical contact areas on top of the first semiconductor die and the perimeter of the second die can be reduced.